Glulam (glued laminated timber) design
Glulam is built up from many thin timber laminations bonded together, which removes the weak points of solid timber and lets it span far further with a clean, exposed finish. We design glulam beams, columns and frames to the Eurocodes for clients across the UK.
How is glulam different from ordinary timber?
Glulam is built up from many thin graded laminations bonded together, which removes the large defects that limit solid timber. The result is stronger, more predictable and available in long, deep or curved shapes, so it spans much further and can be left exposed as a finished structure.
What glulam is and why it performs
Glulam, glued laminated timber, is made by bonding together thin layers of graded softwood, usually spruce, with the grain of every lamination running the same way along the member. Because the boards are thin, drying defects and large knots are removed or dispersed, so the finished beam is far more uniform and reliable than a single sawn section of the same size. That is why glulam reaches design strengths well above solid timber, in strength classes such as GL24h and GL28h, where the number is the characteristic bending strength.
The lamination process also frees the material from the size limits of a tree. Glulam can be made in long lengths, deep sections and, crucially, curved and tapered shapes formed in the press, so it can follow the line of a pitched roof or sweep into an arch. It keeps timber's light weight and low carbon footprint while giving the predictability of an engineered product, and it can be left exposed as a finished, visible structure rather than hidden away, which is a large part of its appeal.
Designing glulam to BS EN 1995
Glulam is designed to BS EN 1995, Eurocode 5, using the same framework as solid timber but with the higher design values of the glulam strength classes and some extra checks specific to the material. Because members are often deep, lateral torsional buckling of the beam and restraint at the compression edge matter, and we check them alongside bending, shear and bearing. The kmod factor for load duration and service class still applies, and for large-volume members a size effect factor adjusts the bending strength, since a very deep beam is statistically more likely to contain a weakness.
Curved and tapered members bring their own checks. Bending a lamination to a radius locks in stresses, and at the apex of a curved or pitched beam the fibres are pulled apart across the grain, so we check tension perpendicular to the grain, a weak direction for timber, and detail reinforcement where needed. Connections are usually the visible detail on an exposed frame, so we design slotted-in steel plates with dowels, or concealed proprietary connectors, to carry the forces while keeping the clean look the material is chosen for.
Fire, moisture and where glulam suits
Glulam behaves well in fire, which surprises people who expect timber to be the weak link. It chars at a slow, predictable rate and the char layer insulates the sound timber beneath, so a large glulam section keeps most of its strength for a useful period. We design for this by adding a sacrificial timber thickness so the reduced section still carries the load for the required fire resistance, which often lets glulam stay exposed where steel would need coating.
Moisture still governs durability. Interior glulam in a dry, heated building is a stable service class one material and needs no protection beyond good detailing. Exposed or humid conditions raise the service class, reduce the design values and call for a suitable adhesive and often a coating, and permanently wet locations are best avoided. Glulam suits open-plan spaces, halls, sports and leisure buildings, canopies, bridges and any structure where long clear spans and a visible timber frame are wanted together. Its main limits are cost against sawn timber and the need to protect long members in transport and on site.
What we check.
The points our calculations resolve for a project like this.
- Strength class selection such as GL24h or GL28h
- Lateral torsional buckling and compression edge restraint on deep beams
- Size effect and volume factors on bending strength
- Tension perpendicular to grain at curved and pitched apex zones
- Slotted steel plate and dowel connections for exposed frames
- Charring rate and sacrificial thickness for fire resistance
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
How is glulam different from ordinary timber?
Glulam is built up from many thin graded laminations bonded together, which removes the large defects that limit solid timber. The result is stronger, more predictable and available in long, deep or curved shapes, so it spans much further and can be left exposed as a finished structure.
Can glulam be left exposed in a fire situation?
Often yes. Glulam chars slowly and the char insulates the timber beneath, so a large section keeps its strength for a useful period. We add a sacrificial thickness so the reduced section still carries the load for the required fire resistance, which frequently avoids the coatings steel would need.
Can glulam be curved?
Yes. The thin laminations are bent to a radius in the press before curing, so glulam can be made curved, tapered or pitched to follow a roof line or form an arch. We add the extra checks these shapes need, particularly tension across the grain at the apex.
Is glulam suitable for outdoor structures?
It can be, with care. For canopies and covered but ventilated locations we raise the service class, specify a suitable adhesive and a coating, and detail to shed water. Permanently wet or fully exposed positions are better avoided or handled with a more durable material. We advise per project across the UK.
Tell us what you are building.
Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
Start a project